1. Field of the Invention
The present invention relates to a piezoelectric device for use in a resonator filter, an actuator, or other suitable apparatus, and a method of producing the same, and more particularly to a piezoelectric device operable to excite bending vibration in the longitudinal direction utilizing a piezoelectric longitudinal effect.
2. Description of the Related Art
There have been proposed different types of piezoelectric devices utilizing a piezoelectric longitudinal effect and those utilizing a piezoelectric transverse effect as piezoelectric resonators and piezoelectric actuators. When an electric field is applied to a piezoelectric member in the same direction as the polarization direction, the piezoelectric longitudinal effect makes use of the displacement of the piezoelectric member in which the piezoelectric member is expanded and contracted in the longitudinal direction, that is, in the direction of the piezoelectric member to which the electric field is applied. The piezoelectric transverse effect makes use of the displacement in which a piezoelectric member is expanded and contracted substantially perpendicularly to the direction in which an electric field is applied, that is, in the transverse direction of the piezoelectric member.
As piezoelectric resonators which are operable in several hundred kHz bands, resonators which carry out radial vibration utilizing a piezoelectric transverse effect or length expanding/contracting vibration have been widely used. In the case of a piezoelectric resonator utilizing the extending vibration, the displacement is used which is generated when an electric field is applied in the thickness direction of a square piezoelectric plate, so that the piezoelectric plate is expanded and contracted in the diameter direction. Moreover, in the case of a piezoelectric resonator utilizing the length expanding/contracting vibration, an electric field is applied to a rod-shaped piezoelectric member polarized only in the thickness direction, in the polarization direction of the piezoelectric member, and thereby, the piezoelectric member is expanded and contracted in the longitudinal direction.
Japanese Unexamined Patent Application Publication No. 10-4330 discloses a lamination type piezoelectric resonator which is operable to excite length expanding/contracting vibration utilizing a piezoelectric longitudinal effect. In this case, a plurality of internal electrodes are arranged substantially perpendicularly to the longitudinal direction in a piezoelectric member which is longer in one direction. Adjacent piezoelectric layers in the longitudinal direction via the internal electrode are polarized 180° out-of-phase with each other in the longitudinal direction. In the piezoelectric resonator, a voltage is applied to the respective piezoelectric members, and thereby, the piezoelectric member is expanding/contracting-vibrated in the longitudinal direction.
According to the piezoelectric resonator which is operable to excite the length expanding/contracting vibration utilizing the above-described piezoelectric longitudinal effect, the band width can be increased compared to a prior art piezoelectric resonator using the piezoelectric transverse effect. Moreover, the piezoelectric resonator utilizing the longitudinal effect has a lamination structure, and therefore, can be constructed so as to have different electrostatic capacitances. Moreover, the piezoelectric resonator utilizing the piezoelectric longitudinal effect can be reduced in size compared to the piezoelectric resonator utilizing the piezoelectric transverse effect.
The size of the piezoelectric resonator utilizing the piezoelectric longitudinal effect can be reduced compared to that of the piezoelectric resonator utilizing the piezoelectric transverse effect, as described above. However, the resonance frequency of the piezoelectric device depends on the length thereof. Thus, to realize a piezoelectric device having a desired resonance frequency, the device must be set to have a predetermined length. Accordingly, the length of the device can not be still more reduced. That is, in the case of the piezoelectric resonator utilizing length expanding/contracting vibration due to the piezoelectric longitudinal effect, the size can not be more reduced.